Absorbent articles for body fluids such as paper diaper and sanitary napkin basically comprise a liquid-permeable surface layer arranged on the side facing to the body skin, a leakproof layer arranged on the side farther from the body skin and an absorbent portion for body fluids arranged there between.
In these articles, a variety of constructions are known for the absorbent portion for body fluids and mainly an absorbent paper made of highly absorbent polymer, flocculent pulp (flap pulp), crepe paper or the like is used as an absorbent material. In accordance with recent progress in the technology of highly absorbent polymer, it has become possible to construct the absorbent portion for body fluids in a thinner form, and thus, body fitness of the absorbent portion of the product has been improved and leakage of body fluids has been lessened.
The improvement in the absorbent property of the product triggers a demand of further development of a new product being in a thinner form and having a larger absorption capacity and longer wearability by consumers.
In order to fulfill such a demand, it is necessary that the absorbent portion for body fluids must absorb all volume of, for example, urine excreted many times. However, as urination is repeated, the rate of absorption of the absorbent portion for body fluids becomes slower, and in particular, absorption of body fluids often does not extend to the end part of the longitudinal direction of the absorbent portion for body fluids. This is considered to be due to insufficient diffusion of body fluids to the longitudinal direction (the longitudinal direction of product) and occurrence of a so-called gel blocking phenomenon which blocks wetting expansion due to swelling of the highly absorbent polymer.
In order to solve these phenomena, there are proposed the technique to promote the longitudinal wetting expansion disclosed in Kohyo (Jpn. unexamined patent publication) No. 2000-510031, Kohyo (Jpn. unexamined patent publication) No. 2000-510033 and the like, the technique to block gel blocking of the highly absorbent polymer disclosed in Kohyo (Jpn. unexamined patent publication) No. 2000-510031, Kohyo (Jpn. unexamined patent publication) No. 2000-510033 and the like, the design of both shape of the highly absorbent polymer and the arrangement thereof, the method for securing spaces to be occupied by swelling of the highly absorbent polymer on wetting, and the like.
The use of any methods described above, however, can not provide a satisfactory solution for the problems. Upon consideration of this cause again, the absorbent portion for body fluids of the conventional absorbent articles for body fluids was found to be based on the premises that body fluids from excretory part would wet and extend (diffuse) to the end of the longitudinal direction by making it lengthwise, arranging it along the longitudinal direction of the product, and designing its approximate center to be located at the excretory part of body fluids. Therefore, body fluids practically can not be absorbed by the entire absorbent portion for body fluids as long as body fluids do not diffuse to the longitudinal direction sufficiently.